Method of increasing the productivity of wells



April 27, 1954 o. F. RITZMANN METHOD OF INCREASING THE PRODUCTIVITY OFWELLS Filed May 17. 1949 7 INVENTOR.

OTTO an RIIZJVDCKNN BY w ATTORNEY Patented Apr. 27, 1954 METHOD OFINCREASING THE PRODUC- TIVITY F WELLS Otto F. Ritzmann, Takoma Park,Md., assignor to Gulf Oil Corporation,

ration of Pennsylvania Application May 1'7, 1949, Serial No. 93,750

3 Claims.

This invention relates to wells and means for increasing theproductivity thereof.

An object of the invention is to provide a novel and improved processwhereby, upon the application of the steps of the process to a well, theproductivity thereof may be substantially increased.

Another object of the invention is to provide a novel and improvedprocess for increasing the productivity of oil wells by applyinginternal static pressure to the well in the oil bearing level, and,while maintaining such internal static pressure at a magnitudesufficient to raise the overburden, producing at the oil-bearing level avastly increased instantaneous dynamic pressure to irregularize theopposed interfaces of the cracks in the oil bearing formation enlargedupon raising the overburden, so as to block intermating of such surfacesupon release of said pressures, whereupon oil therein may be withdrawnfrom the well.

A further object of the invention is to provide means for enhancing theproductivity of an oil well comprising means for applying staticpressure to the well in the region of the oil-bearing formation toenlarge incipient fractures and cracks in the oil-bearing formation, andmeans for producing in said well in the immediate level bearing saidoil, an instantaneous shock wave adapted to penetrate said crevices,fractures and cracks and to produce fragmentation of projecting surfacesthereof to block intermating upon release of said pressures and shockwave, whereby passageways are formed to conduct oil from said formationinto said well for withdrawal therefrom.

Still another object of the invention is to providean improved and novelprocess for enhancing the productivity of an oil well by employment ofthe very simple and readily available means of hydrostatic pressure onthe well and detonation of an explosive charge in the well at the levelof the oil-bearing formation.

Other objects and advantages of the invention will become apparent fromthe following description of a preferred embodiment thereof asillustrated in the accompanying drawings, and in which,

Figure 1 is a sectional fragmentary elevation showing a section ofground into which a well has been driven to an oil-bearing formation,with pressurizing means applied to the well according to my invention,but not yet sufficient to lift the overburden, and with an explosivecharge disposed in the well but not yet detonated.

Pittsburgh, Pa., 2. corpo- Figure 2 is a sectional fragmentary elevationsimilar to Figure 1, but showing the situation after my improved andnovel process has been applied to the well, and the explosive charge hasbeen detonated.

The yield of oil from wells bored into oil-bearing formations isfrequently reduced gradually to a rate at which it is uneconomical tocontinue operation of the well unless the production thereof can beincreased in some manner. It often happens that there is sufficient oilin the oil-bearing strata but that various conditions prevent this oilfrom flowing into the oil well itself so that it can ultimately reachthe earths surface for use.

The failure of the oil in the stratum to reach the oil well may be dueto a number of causes, among which are, clogging up of the outlets ofcracks and fissures in the stratum which thus block oil flowtherethrough, and also the fact that many oil-bearing strata arethemselves of a compact and fine-pored structure, such as finegrainedsandstone, which is of such poor permeability that the oil actuallyflowing under such resistance toward the oil well is very small inquantity. Under these conditions, when there is sufficient evidence fromgeological studies and geophysical exploratory devices to clearlyindicate the presence of oil in commercial quantities in the stratumunder study, it is important, in view of the existing financialinvestment in the well itself, that something be done to bring aboutincreased productivity of the well.

This problem has long been under study, and many solutions have beenproposed. For example, it has been submitted that such wells might betreated with acid which might, if all went well, dissolve the stratumsurfaces opening upon the well, so as to permit oil to gush into thewell. However, as is well known to those skilled in the art, such acidtreatment of wells has its disadvantages and may well result insomething less than satisfaction on the part of those owning the wellwhen viewed in the light of the results obtained. Such negative resultsare also often obtained when resort is had to shooting the wellaccording to the prior art methods, which may shatter the oil wellsurface at the oil-bearing level with indeterminable results, and whichfurther may have disastrous consequences, causing leakage of oil throughad- 7 jacent strata with consequent loss thereof entirely.

The present invention proposes an entirely new approach to the problem,wherein first the inherent fissures and cracks in the oil-bearingstratum are enlarged by what may be termed mechanical or hydraulicmeans, sufficiently to permit flow of oil therethrough into the oilwell. Thereafter, and while such fissures and cracks are held. open,additional, instantaneous and high explosive forces are employed rightin the same level as the oil bearing stratum under treatment, not onlyto further enhance the fluid-conducting capacity of such cracks andcrevices, but also to excoriate and abrade their interior surfaces whichhave been forced apart by the hydraulic static pressures appliedthereto, so as to make them incapable of mating contact when suchpressures are ultimately released; As a result, upon release of suchpressures, both static and dynamic, these opened cracks, crevices andfissures in the oil-bearing formation remain open for conducting oilfrom the formation into the well itself, from which it may be recoveredby well-known means.

In order to understand clearly the nature of the invention, and the bestmeans. for carrying it out, reference may now be had to the drawings,

in which like numerals denote similar parts and formations throughoutthe several views.

Figures 1 and 2 both show a sectional elevational view in fragment, ofearth into which has been driven a bore in forming an oil well. The wellpasses through a number of strata disposed vertically above eachv other,such as those shown at !2, l4, l6 and i8. As illustrated, the lower endof the well it) terminates after extending only partly through the lowerstratum 8, to the level 20.

Thus, the stratum 22 may be earth or soil, and the layer 14 may be ofsome other material, such as an impervious cap rock in the nature ofshale and the like. Directly below the top stratum 12 the drawing showsa broken area 22 which is merely to indicate that other intermediatestrata may be disposed between the layers I2 and i4, and, as is wellknown in the art, the vertical distance between the earth's surface 24and the lower level of the stratum l4 may'actually be on the order ofseveral thousand feet, such intermediate and well-known strata beingomitted from the drawings only for purposes of clarity of illustration,since they are well known in the art, and form no important part of theinvention if as such.

In the course of drilling the well l0, it is assumed that the stratum 16has been found or determined. by well-known methods, to be oil bearing.Incipient cracks or fissures 25 radiate outwardly from the inner surface28 of the well bore 10, between the top level 39 of the oil-bearingstratum i6 and its lower level 32. Although, for purposes of clarityonly, six such incipient cracks or fissures 26 are shown in Figure 1, itwill be understood that such cracks and fissures 26 may be large innumber, and running in all possible directions and at all angles, andextending in the oil-bearing stratum for considerable distances from theoil well bore in itself.

Further, it will be observed that for purposes of illustration only,these incipient fissures and cracks 25 in Figure 1 are not shown asirregular, but it will be understood that actually they may be quiteirregular, undulating, and undoubtedly will intersect with adjacentincipient cracks and fissures at many points and, indeed, theseincipient cracks may merely be lines of weakness in the oil-bearing rockwhose tensile strength is usually not very great.

Inside the oil-bearing at the producing formation it.

formation It, there will also be localized regions B l of high oilconcentration, which are normally out of direct communication with theoil well ii), and betr een which it is desired to open communication sothat the oil in such regions 35 may flow freely into the well.

As shown diagrammatically in Figure l, a tubular pipe or casing 36extends downward into the well Hi, from the earths surface it, throughall the intervening strata E2, M3 and those indicated by the broken area22, the lower end portion 38 of the casing having an outwardly flangedcasing seat in or just above the oil-bearing stratum l6, and tightlysealed by means of cement or any suitable well-known sealing substance40 forming a gasket against leakage around the outor surface of the wellcasing. The cement G0 is shown rising only a short distance in theannular space outside the casing but may rise many hundreds of feet oreven fill the annular space all the way to the surface 24. A well head 22 is secured to the top of the well casing, closing the same, and aso-called lubricator or air lock head in the form of a hollowcylindrical closed housing 44 is secured to the well head 42 through aninterconnecting gate diagrammatically shown at -16 which is lined withresilient material (not shown) forming a gland packing to accommodateslidably without leakage a suspension cable 28, but which may be openedto permit larger tools to be introduced into the well. A similar gate isshown diagrammatically at 47. While for purposes of illustrating myinvention I have shown the equipment at the top of the well connectingdirectly with the casing, it is to be understood that this equipment mayalternatively be connected to high pressure tubing (not shown) in thewell, such tubing being anchored and sealed to the casing in its lowerreaches by means of a packer and expanding slip jaws in wellknownmanner.

upper end of the cable #28 is secured to hoisting apparatus of anywell-known type, for lowering into the well an explosive device 59. Thedevice Eii may be lowered into the well through the lubricator 5 3. oralternatively the lubricator may be dispensed with and the device 5Qlowered into the well prior to pressurization. The device 58 may be inthe form of a housin containing an explosive charge, and means fordetonating the charge, and it will be understood that the detonator maybe electrically actuated if desired, by means of current supplied fromsource within the housing it and actuated by automatic timing means, orby current supplied by wires included in the suspension cable 48.

According to a preferred form of my process, I. fill the well with fluidsuch as water, andi crease the pressure cfv the fluid in the weli bypumping from a fluid source 52 by means of a pump indicated at and ofany well-known type. Pumping is continued until the pressure in the wellhas been raised to a previously-calculated pressure sufficient to liftthe overburden By the term overburden is meant the overlying rocksbetween the formation it and the surface of the earth 24. Apressure-indicating instrument is shown at in the fluid inlet E8.

The pressurizing fluid 55 may be an aqueous fluid, but I have found itto be advantageous to fill the lower portion of the well, contiguous tothe oil-producing formation, with a slug of oil 52, which may thusextend from the floor of the well 26, approximately to. the level shownat B4,

the-oil 62 being sufficiently dense to remain at the position indicated.Sufiicient hydrostatic pressure to lift the overburden may be obtainedwith relative ease because to the pressure applied at the surface thereis automatically added the hydrostatic head of the column of well fluidwhich may be weighted to have a high density as is well known in theart. The first stage pressurization by means of the pump 54, the amountof which is easily computed from the density of the overlying rocks andthe fluid in the well may, according to one calculation for a typicalwell of average depth, have a pressure of between about 1000 to 2000pounds per square inch at the oil-producing level. A pressure slightlyabove that needed to just lift the overburden appears desirable, and itwill be found that by thus hydraulically lifting the overburden at theoil-producing stratum, the incipient cracks, fissures and crevices 26will be opened at many places in this stratum, so that passageways areformed through which the oil in the blocked pockets 34 may flow into thewell bore.

However this flow will not take place while this very high staticpressure is being maintained, and, if the pressure is released, theoverburden will settle once again, and the opposed surfaces of thecracks and fissures will mate with each other so they will again close,blocking flow of oil therethrough. Accordingly, while the overburden isin such raised position, with the incipient cracks and fissures opened Iapply a vastly increased instantaneous shock wave to these cracks andfissures by detonating the explosive device 50, with the result that theinterior juxtaposed surfaces of the cracks and fissures are broken up tosuch an extent that they will no longer mate when all pressure isreleased, and further, broken off chunks of rock will lodge at variouspoints in such cracks so as to hold them open.

When the pressure is again released, these cracks and fissures, nowenlarged in size and cross section, and held open by their irregular andnon-mating surfaces, and by broken off particles of rock lodgedtherebetween, will form open passageways for oil in the formation toflow to the well bore 10. In a deep well hole, the explosion of thedevice 50 may merely produce a momentary shock at the surface, and ifthe shot is effective there will be a drop in well-head pressure due tofluid passing out into the formation through the enlarged cracksproduced. The well is afterward put on production in any conventionaland well-known manner.

Figure 2 shows more clearly the situation immediately after theexplosive charge 50 has been detonated. "It will be seen that the cracksand crevices 26a have been quite substantially enlarged by theapplication of the static pressure by means of the pump 54 which liftedthe overburden, and that as a result of the vastly increasedinstantaneous explosive detonation and shock wave from actuation of thedevice 50, the opposed surfaces of each of the cracks and crevices 26ahave been made quite irregular and no longer mate with each other, sothat they prop the cracks open. Further, it will be understood thatbroken-01f chunks of rock will be broken off from thesev crevicesurfaces and become lodged therebetween, so as to assist in proppingthem open. The pumping equipment and lubricator 44 of Figure 1 are notrepeated in Figure 2, being omitted therefrom.

While the main explosive charge in the hous- 6 I ing 50 may benitroglycerine, it will be understood that other well-known explosivesmay also be employed, these being preferably placed inside the housingwhich may be designed to withstand the pressure applied by the pump 54,prior to detonation. By use of such a housing forming .a bomb, the bombfragments will also be forced into the opened crevices in the formation,and will assist in holding them open. The cable 48 may be dispensedwith, if desired, and the bomb 5!! arranged for dropping down the wellwhile it is under pressure, for detonation upon hitting bottom, or aftera time interval has elapsed.

Although I have described my invention in specific terms, it will beunderstood that various changes may be made in the selection of theparts and means for carrying the same out, and in their arrangement,within the spirit and scope of the invention as defined by the appendedclaims.

I claim:

1. A process for increasing the productivity of an oil well whichpenetrates an oil-bearing rock formation under cover of an overburdenand in which communication between oil-bearing regions of said formationand said oil well is at least partially blocked, which comprises fillingsaid oil well at said oil-bearing formation with a liquid, placing insaid liquid opposite said formation an explosive charge, applying tosaid liquid sufiicient hydraulic pressure to raise the overburden,thereby opening cracks and fissures in said formation between the welland oil-bearing regions of said formation, and detonating said explosivecharge while maintaining said hydraulic pressure, whereby the interiorsof said cracks and fissures are subjected to a high-intensity shock wavesufiicient to irregularize opposed surfaces of said cracks and fissuresto block mating thereof and to break off therefrom rock fragments tolodge therebetween, and thereupon releasing said hydraulic pressure,whereupon said opened cracks and fissures in said formation remainpropped open to form passageways communicating between said oil-bearingregions and said oil well, and whereupon said oil in said regions isfree to enter said oil Well.

2. A process for increasing the productivity of an oil well whichpenetrates an oil-bearing rock formation under cover of an overburdenand in which communication between oil-bearing regions of said formationand said oil well is at least partially blocked, which comprises fillingsaid oil well at said oil-bearing formation with a liquid compatiblewith oil, placing in said liquid opposite said formation an explosivecharge, applying to said liquid sufficient hydraulic pressure to raisethe overburden, thereby opening cracks and fissures in said formationbetween the well and oil-bearing regions of said formation, and, whilemaintaining said hydraulic pressure, detonating said explosive charge toproduce a highorder detonation and shock wave at the level of saidoil-bearing formation, said disturbance acting violently upon theinteriors of said opened-up cracks and fissures to irregularize theopposed surfaces to block intermating thereof and to break off therefromrock fragments to lodge therebetween, and thereupon releasing saidhydraulic pressure, whereupon said opened cracks and fissures in saidformation remain propped open to afford communication between saidoil-bearing regions of said formation and the interior of said oil well.

3. A process for increasing the productivity of 81 References Citedinthefile .of this patent UNITED' STATES PATENTS" Number 5 Re. 5,4341,248,689 2,034,568 2,171,416 2,316,596 10 2,379,516

Name Date Roberts June-3, 1873: McAvoy Dec.'4, '191'7 Ferrell et a1 Mar.1'7, 19361 Lee Aug; 2.9;1939- Kennedy Apr; 13, 1943- Garrison July3,-'1'945

